The present invention relates to a method of making laminated containers whose peripheral walls are composed each of an outer layer and an inner layer disposed therein to be delaminated therefrom. The invention relates also to a method of forming at least one hole solely in the outer layer constituting an injection-laminated parison or the like used to blow mold a delaminatable container.
Japanese Patent Laying-Open Gazette No. Hei. 4-267727 discloses a laminated container having a delaminatable layer designed such that ambient air is inhibited from entering the container through a mouth while allowing its content to be discharged. This container is composed of an impermeable inner layer and a squeezable outer layer, wherein the inner layer can be readily delaminated from the outer layer in which at least one ventilation hole is formed such that the ambient air can communicate with the space between the layers. In this way, the inner layer will spontaneously shrink as quantity of the content decreases, with the ambient air flowing into the space through said hole so that only the outer layer can restore its normal configuration. Its content remains satisfactory in quality, from the beginning to end of use, without being impaired by air or light beams.
The direct blow molding known in the art may be an example of the method of manufacturing laminated bottles of this kind. In this method, a multi-layer extruder is used to extrude an inner resin layer and an outer resin layer laminated thereon to form a cylindrical parison. This parison will be placed in a blow forming mold (and pinched off to provide a closed bottom in a finished bottle), axially stretched and simultaneously blow molded, to thereby give the finished bottle having the delaminatable inner layer.
In the described prior art laminated bottles, their inner layers should have each a highly precise wall thickness. In particular, evenness in wall thickness is more strictly required for profiled or xe2x80x98modified cross sectionxe2x80x99 bottles such as elliptic bottles. In order to meet such a requirement, the so-called xe2x80x98injection blow-moldingxe2x80x99 method is preferable wherein a laminated parison that has been prepared by injection molding will be blow molded.
In many cases, the described laminated bottles are used as containers for holding therein certain liquids (such as hair-dye) that are likely to change in their properties due to contact with air. Selection of a resin material for forming the inner layer must be done carefully lest the content should undergo any noticeable deterioration even if stored for a long time. Further, the material is to be selected from relatively soft ones because the inner layers have to gradually shrink during use. Examples of materials satisfying these conditions may be polyolefin resins such as a polypropylene and a polyethylene. Polyolefin resins are highly resistant to chemicals and almost impermeable for gases. Certain medically active ingredients prone to deteriorate due to expiration of water vapor are protected from deterioration. A xe2x80x98PETxe2x80x99 or the like resin may be preferred as a material for forming the outer layer.
Polyolefin such as polyethylene have lower melting points than saturated polyesters such as PET. If the injection-stretching method accompanied by the subsequent blow-molding step is applied to preparation of a laminated parison wherein an inner preform is injected prior to injection of an outer preform, then the following problem would occur. Since the thermal deformation temperature of the already prepared inner preform is lower than the molding temperature for the outer preform, the inner preform will probably melt when molding the outer preform, failing to manufacture useful multi-layer preforms.
Since the inner layer of said laminated container will gradually shrink as its content is consumed, it is desirable that the outer and inner layers firmly engage with each other at bottom in order to smoothen the shrinkage of inner layer. It is described in the above Gazette that the outer and inner layers are fixed on each other at their bottoms, but not teaching how to do this. On the other hand, Japanese Utility Model Publication No. Hei. 7-48519 shows a pinched-off ridge that is formed in the container bottom so as to unite the outer layer with the inner layer. In detail, when blow molding the container, a raw multi-layer preform that has been extruded from a molding apparatus through a nozzle thereof will be pinched off in such a manner that mutually-engaging corrugations are formed by pressing bottom portions of the layers sideways. This structure will provide the outer and inner layers firmly bonded to each other, though an extra additional device is necessary to press the bottom portion, failing to match the injection-stretching-blow-molding method.
A first object of the present invention is therefore to provide a method of making a laminated bottle by injection molding a laminated parison that will subsequently be blow molded smoothly to form the bottle of an improved quality, wherein optimum materials are chosen for an inner layer and an outer layer, respectively. Another object is to facilitate the inner layer to be easily combined in part with the outer layer.
A user may close with his or her finger(s) a ventilation hole(s) that is(are) formed in the prior art delaminatable container for introducing ambient air in between its layers. Alternatively, a film tag may be adhered in part to the rim of the ventilation hole so that the tag larger than the hole is disposed inside the outer layer. Such a kind of valve will allow the air to flow inwards through the outer layer, but not through the inner layer. With the container being gripped by the user, the ventilation hole will be closed with his or her fingers or by the valve so as not to allow any amount of air to leak out from the interlayer space. Such a depressed outer layer will cause the interlayer air to press in a centripetal direction the inner layer to exude the content out of the container.
In the prior art of this type, whether accompanied by the valve or not, the outer layer having the ventilation hole(s) has generally been blow molded or hot molded before integrating the inner and outer layers one another. Alternatively, a protrusion jutting from the inner wall defining a blow-molding cavity has served to directly form a ventilation hole or to form a groove readily transformable into a hole.
The prior art method consisting of the steps of preliminarily blow molding the outer layer and subsequently integrating it with the inner layer does however require so many steps as raising manufacture cost of the delaminatable containers and lowering yield thereof. The lug protruding inwardly from the inner wall defining the blow-molding cavity is described as a means useful to form the ventilation hole solely in the outer layer. However, there is a possibility that such a lug would injure the inner layer. The forming of such a preliminary groove in the outer layer may be possible, but semi-finished containers have to be after-treated one by one with hand to transform them into the holes. Operation efficiency in manufacture of those containers will thus be lowered, raising manufacture cost. Also disadvantageously, the late opening of the hole in the outer layer is likely to damage the inner layer.
A second object of the present invention is to provide a method of making a laminated bottle in such a manner that at least one ventilation hole can be formed easily and surely in an outer layer, without any fear of injuring an inner layer, and more particularly to provide a method of forming at least one hole only in the outer layer of an injection molded laminated article such as a parison for use to blow mold a laminated container having the delaminatable inner layer.
The present invention provides a method of making a laminated bottle having a outer layer and a inner layer laminated on an inner surface of the outer layer so as to be capable of delaminating from the surface. The present method may comprise the steps of injection molding a preform for the outer layer by injecting a molten first resin, then injection molding inside the preform a further preform for the inner layer by injecting a molten second resin so that the preforms comprise a parison, and finally blow molding the laminated bottle by blowing the parison. In this method, the second resin may have a melting point lower than that of the first resin.
In the method of the present invention, a injection mold may be used for said injection molding of the inner preform, the mold comprising a core segment and a cavity segment, the core segment having an injection gate formed therein. Furthermore, injection molding the inner preform may comprise the steps of loading the outer preform in the cavity segment, subsequently clamping the core segment and the cavity segment, and finally injecting the second resin inside the outer preform through the gate in the core segment.
Also in the method of the present invention, the method may further comprise the step of forming a through-hole in the outer preform being injection molded. The through-hole may preferably be formed at a portion thereof facing an injection gate for injecting the second resin.
It may be possible that injection molding the inner preform comprises injecting the second resin through the gate and also the through-hole to flow along an inner surface of the outer preform.
Further in the method of the present invention, the through-hole may be formed by a first pin, the pin projecting toward a further injection gate for injecting the first resin through it after injecting of the first resin has been finished so that an end portion of the pin strikes the further gate.
Further in the method of the present invention, a flange may be formed of the second resin when injection molding the inner preform, such that the flange formed integral with the inner preform is located outside the through-hole formed in the outer layer.
In the method of the present invention, the inner preform may be injection molded so as to a bulge of the second resin is formed, the bulge projecting through the through-hole from the outer preform. Furthermore, a stretching rod used for longitudinal stretching the parison may depress and collapse the bulge at said blow molding.
In the method of the present invention, the inner preform may be injection molded to be integral with a plurality of thickened portions extending vertically at angular intervals.
Also in the method of the present invention, the inner preform may be injection molded to have a body that is formed integral with at least one thickened portions extending in a helical direction.
The present invention is applicable to make the laminated bottle having at least one ventilation hole to allow ambient air to flow in between the outer and inner layers. In this case, such ventilation hole may be formed at the step of injection molding the outer preform, and when the inner preform is subsequently injection molded, a second pin may have been inserted from outside and through the outer preform in such a manner that an end portion of the second pin is held substantially in flush with the inner surface of the outer preform.
In the method of the present invention for manufacture of the laminated bottle having the ventilation hole, a cavity segment and a first core segment for molding the outer preform may be used for injection molding the outer preform. Preferably, this method further comprising the additional step of replacing the first core segment with a second core segment for molding the inner preform, without removing the outer preform out of the cavity segment, with the additional step being interposed between the steps of injection molding the outer and inner preforms. The cavity segment and the second segment may be used for injection molding the inner preform. Furthermore, forming the ventilation hole may comprise striking the second pin against the first core segment before the resin of the outer preform cures at the step of injection molding the outer preform. The ventilation hole preferable remain closed with the second pin during injection molding the inner layer.
Additionally, the second pin may be capable of shifting between its projected position where the pin strikes the first core segment clamped to the cavity segment and its retracted position where the pin is embedded in the cavity segment.
Also in the method of the present invention, the outer preform may be held by a lip mold all through the first, second and third steps. In this case, the second pin may be capable of shifting between its projected position where the pin strikes the first core segment clamped to the cavity segment and its retracted position where the pin is embedded in the lip mold. The pin at the projected position will clog the ventilation hole but the pin at the retracted position leaves the hole opened.
Further in the method of the present invention, a first injection mold may be used for injection molding the outer preform and a second injection mold is used for injection molding the inner preform. Further, this method preferable comprises the steps, between the steps of respectively injection molding the outer and inner preforms, of releasing the outer preform from the first mold, loading the released outer preform into the second mold, inserting the pin into the ventilation hole that has been formed in the outer preform. The pin may remain left is the ventilation hole during injection molding the inner layer.
In the method of the present invention, the parison may be blow molded such that the stretching for orientation of the preforms is conducted for the portion thereof located below the ventilation hole.
Also this invention proposes a method of making at least one hole solely in an outer layer of an injection molded laminated product having an inner layer formed on an inner surface of the outer layer, the method comprising:
the step of injection molding the outer layer, and the step of subsequently injection molding the inner layer using a resin whose melting point is lower than that of a further resin forming the outer layer,
wherein the at least one hole is formed during the step injection molding the outer layer,
and the inner layer is injection molded such that an inner end of at least one pin inserted from outside is temporarily located substantially in flush with the inner surface of the outer layer.